HIV infection of the CMS often results in the development of severe neurological complications, including HIV-associated dementia (HAD). The number of activated macrophages in the CMS appears to be a much better indicator of HAD than viral load, suggesting that leukocyte infiltration and dementia are tightly correlated. The process by which infected monocytes, and perhaps T cells, cross the blood brain barrier (BBB) and infiltrate the CMS is still not well understood. It is believed that under non-pathological conditions, the transmigration of leukocytes across the CMS vasculature does not disrupt the BBB because specific homophilic and heterophilic interactions between adhesion molecules, adherens junction and tight junction proteins (termed "cell junction proteins") on leukocytes and BBB cells maintain the impermeability of these vessels during leukocyte diapedesis. However, during the pathogenesis of HAD, leukocyte infiltration of the CMS is associated with BBB compromise. Thus the molecular interactions inherent in leukocyte diapedesis across the BBB are altered, resulting in increased BBB disruption. We have the novel finding that HIV-infected PBMC have an enhanced capacity to transmigrate across our tissue culture model of the BBB in response to CCL2, but not to other chemokines. This enhanced transmigration is associated with high expression of the CCL2 receptor, CCR2, and alterations in cell junction proteins in HIV-infected leukocytes. It is therefore our hypothesis that these alterations result in aberrant leukocyte/BBB cell interactions upon exposure of HIV-infected leukocytes to CCL2 during the process of transmigration, leading to enhanced migration and barrier disruption. To address this hypothesis we will;1) analyze early events of HIV-infected PBMC transmigration and the kinetics of BBB disruption, 2) examine changes in matrix metalloproteinases (MMPs) and cell junction protein expression in BBB cells or HIV-infected PBMC after CCL2 treatment, 3) determine the contribution of cell junction proteins during the process of HIV- infected PBMC transmigration, 4) analyze complex formation between cell junction and intracellular adaptor proteins associated with junctional complex anchoring to the cytoskeleton during the process of HIV- infected PBMC transmigration, and 5) examine SIV infected macaques as an animal model of NeuroAIDS for the dynamic sequence of events that result in neurological dysfunction.